80 THE FLOWERING PLANT. 
cyme may also be three-rayed, four-rayed, &c., when three, four, 
&c., lateral branches overtop the main axis. (2.) The nature 
of a pseudaxis or sympodium has already been fully explained 
(pp. 24, 48). The pseudaxis may either be formed by branches 
developed on either side alternately, when it is scorpioid, or by 
branches belonging to one side only, when it is helicoid. The 
vegetative shoots of elm, &c., and flowering shoots of deadly 
nightshade are instances of the former, while forget-me-not 
illustrates the latter case, where the pseudaxis naturally curls 
round in a spiral way (fig. 36). 
Compound cymes are distinguished by the fact that branches 
of secondary or higher order themselves bear cymes instead of 
terminating in flowers. Elder is a common example. A com- 
pact cyme is termed a /ascicle, and if so condensed as to look like 
a capitulum, it is a glomerulus. 
Mixed inflorescences, which combine more or less the racemose 
and cymose types, are not uncommon. As might be expected, 
flower clusters of this nature are usually compound. Compara- 
tively few special names have been given to these cases, since it 
is easier to describe the general and partial ways of branching 
separately. The heads of Composites, for example, are often 
arranged in a cymose manner. Panicles are frequently mixed, 
and the general name ¢hyrsus has been given to elongated com- 
pact forms in which the primary branching is racemose and the 
secondary cymose, as in the flowering shoots of lilac and horse- 
chestnut. The verticillaster is a variety of thyrsus found in some 
plants, such as dead nettles, where the leaves are opposite and 
decussate. At first sight there appears to be a circlet of flowers 
at each node, the uppermost circles being youngest, so that the 
general arrangement is racemose or indefinite. Careful exami- 
nation shows, however, that each apparent circlet is in reality 
composed of two very short cymose flower clusters in the axils of 
the opposite leaves. 
The ‘flower, as a whole, generally displays a certain symmetry, 
as seen on ground-plan, It is usually either radially symmetrical 
or bilaterally symmetrical (cf. p. 52).! In the latter case the median 
or antero-posterior plane is in most cases the one which divides it 
into similar halves. 
Lastly, a flower may be asymmetrical, when it is not divisible 
by any plane into similar halves. Flowers coming under the 
second and third cases may conveniently be called zrregular. In 
determining the irregularity or otherwise of a flower, calyx and 
1 Radially symmetrical flowers are also termed regular, polysymmetrical, or 
actinomorphic, and bilaterally symmetrical ones zygomorphic or monosym- 
metrical, 
